Why is bean paste a bit bitter?

Bean paste can't be without bitterness, and the bitterness is cinnabar; The advantage of casserole stew is that the taste is not so easy to leak out. So the raw material of red bean paste you stewed is cinnabar beans, and cinnabar was also added during the firing of purple casserole. In this way, not only the cinnabar in the braised bean paste is not completely dispersed, but also a small amount of cinnabar is volatilized from the teapot after you stew it for so long, which will of course aggravate the bitterness. I suggest you cook in an iron pan. Although I don't know what your ideal red bean paste effect is, I have made it myself three or four times and the effect is not bad.